Micro surgical instrument and loading unit for use therewith

ABSTRACT

A loading unit for engagement with a surgical instrument. The loading unit includes a proximal body portion, an end effector, an actuation sled, and pushers. The actuation sled is longitudinally translatable within a cartridge assembly. The pushers are disposed within the cartridge assembly. Each pusher includes a camming surface configured for engagement with the actuation sled. The camming surface of each pusher in a first row is longitudinally aligned with the camming surface of each pusher in a second row. The first row of pushers is laterally offset from the second row of pushers.

BACKGROUND Technical Field

The present disclosure relates generally to instruments for surgically joining tissue and, more specifically, to a surgical fastening instrument and a loading unit including an end effector having a relatively small diameter.

Background of Related Art

Various types of surgical instruments used to surgically join tissue are known in the art, and are commonly used, for example, for closure of tissue or organs in transection, resection, anastomoses, for occlusion of organs in thoracic and abdominal procedures, and for electrosurgically fusing or sealing tissue.

One example of such a surgical instrument is a surgical stapling instrument, which may include an anvil assembly, a cartridge assembly for supporting an array of surgical fasteners, an approximation mechanism for approximating the cartridge and anvil assemblies, and a firing mechanism for ejecting the surgical fasteners from the cartridge assembly.

Using a surgical instrument, it is common for a surgeon to approximate the anvil and cartridge members. Next, the surgeon can fire the instrument to emplace surgical fasteners in tissue. Additionally, the surgeon may use the same instrument or a separate instrument to cut the tissue adjacent or between the row(s) of surgical fasteners.

Additionally, a loading unit (e.g., a single use loading unit or a disposable loading unit) may be attached to an elongated or endoscopic portion of a surgical stapling instrument. Such loading units allow surgical stapling instruments to have greater versatility, for example. The loading units may be configured for a single use, and/or may be configured for multiple uses.

Further, end effectors and/or loading units are generally limited in size by various components contained therein. That is, while there may be a need for end effectors and/or loading units having diameters that are smaller than those typically available, the diameter of the end effector and/or loading unit is typically limited by the size, geometry and/or orientation of the staple pushers, I-beam, actuation sled, and fasteners, for example, contained therein.

SUMMARY

The present disclosure relates to a loading unit configured for engagement with a surgical instrument. The loading unit includes a proximal body portion, an end effector, an actuation sled, and pushers. The proximal body portion defines a longitudinal axis. The end effector is disposed in mechanical cooperation with the proximal body portion, and includes a cartridge assembly and an anvil assembly. One of the cartridge assembly and the anvil assembly is movable with respect to the other of the cartridge assembly and the anvil assembly between an open position and an approximated position to capture tissue therebetween. The cartridge assembly is configured to house fasteners therein. The actuation sled is longitudinally translatable within the cartridge assembly. The pushers are disposed within the cartridge assembly. The pushers are arranged in first and second rows. Each pusher includes a camming surface configured for engagement with the actuation sled. The camming surface of each pusher in the first row is longitudinally aligned with the camming surface of each pusher in the second row. The first row is laterally offset from the second row.

In disclosed embodiments, the one camming surface of each pusher includes a first camming surface and a second camming surface. It is further disclosed that the actuation sled is configured to contact the first camming surface of each pusher in the first row during distal translation of the actuation sled, and that the actuation sled is configured to contact the second camming surface of each pusher in the second row during distal translation of the actuation sled. Additionally, the second camming surface of each pusher in the first row is spaced apart from the actuation sled during distal translation of the actuation sled, and the first camming surface of each pusher in the second row is spaced apart from the actuation sled during distal translation of the actuation sled.

It is also disclosed that the pushers are arranged in a third row and a fourth row. Further, the actuation sled includes a first wedge and a second wedge. Distal translation of the actuation sled causes the first wedge to contact the camming surface of each pusher in the first row and the second camming surface of each pusher in the second row. Distal translation of the actuation sled causes the second wedge to contact the first camming surface of each pusher in the third row and the second camming surface of each pusher in the fourth row.

It is further disclosed that an outer-most diameter of the end effector is about 5 mm.

In disclosed embodiments, the loading unit includes a plurality of T-shaped retention slots extending through a tissue-contacting surface of the cartridge assembly.

It is also disclosed that each pusher in the first row is disposed in a first orientation, and each pusher in the second row is disposed in a second orientation. The first orientation is offset 180° from the second orientation.

Further, it is disclosed that each pusher in the first row is the same as each pusher in the second row.

In disclosed embodiments, the first camming surface is disposed at a first angle with respect to the longitudinal axis, the second camming surface is disposed at a second angle with respect to the longitudinal axis, and the first angle is the same as the second angle. It is disclosed that the first angle is between about 20° and about 40°.

It is further disclosed that each pusher includes a body portion including an upper edge configured to engage a fastener, a lateral extension extending perpendicularly from the body portion, a first leg extending in a first direction from the lateral extension and having a first camming surface, and a second leg extending in a second direction from the lateral extension and having a second camming surface. The upper edge of the lateral extension is co-planar with the upper edge of the body portion.

The present disclosure also relates to a pusher for use with a surgical instrument. The pusher includes a body portion, a lateral extension, a first leg and a second leg. The body portion includes an upper edge configured to engage a fastener. The lateral extension extends perpendicularly from the body portion. The first leg extends in a first direction from the lateral extension and includes a first camming surface. The second leg extends in a second direction from the lateral extension and includes a second camming surface.

In disclosed embodiments, an upper edge of the lateral extension is co-planar with the upper edge of the body portion.

It is further disclosed that the first camming surface is disposed at a first angle with respect to the longitudinal axis, the second camming surface is disposed at a second angle with respect to the longitudinal axis, and the first angle and the second angle are the same. Additionally, it is disclosed that the first angle is between about 20° and about 40°. It is also disclosed that the first direction is opposite from the second direction.

BRIEF DESCRIPTION OF FIGURES

Various embodiments of the presently disclosed surgical instruments and loading units are disclosed herein with reference to the drawings, wherein:

FIG. 1 is a perspective view of a surgical instrument in accordance with an embodiment of the present disclosure;

FIG. 2 is a perspective view of a loading unit having an end effector in accordance with the present disclosure;

FIG. 3 is a perspective view of the loading unit of FIG. 2 illustrating the end effector disposed in an articulated position;

FIG. 4 is a perspective view of the end effector of FIG. 3 in an open position;

FIG. 5 is a side view of the end effector of FIG. 4 in an approximated position;

FIG. 6 is a top view of a cartridge assembly of the end effector of FIG. 4;

FIG. 7 is an assembly view of the end effector of FIG. 4;

FIG. 8 illustrates the area of detail indicated in FIG. 7;

FIGS. 9 and 10 are perspective views of an anvil assembly of the end effector of FIG. 4;

FIGS. 11 and 12 are perspective views of a sled, pushers, and fasteners of the loading unit according to the present disclosure;

FIG. 12A is a perspective view of a pusher of FIGS. 11 and 12;

FIG. 13 is an assembly view of a portion of the anvil assembly and a spring of the loading unit of the present disclosure;

FIG. 14 is a perspective view of the proximal portion of the anvil assembly engaged with the spring of FIG. 13;

FIG. 15 is a side cross-sectional view of portions of the end effector taken along line 15-15 of FIG. 4;

FIG. 16 illustrates the area of detail indicated in FIG. 15;

FIG. 17 is a side cross-sectional view of portions of the end effector taken along line 17-17 of FIG. 4;

FIG. 18 illustrates the area of detail indicated in FIG. 17;

FIG. 19 is a perspective view of the end effector of the present disclosure in an approximated position;

FIG. 20 is a perspective view of a portion of the end effector of FIG. 19;

FIG. 21 is a side cross-sectional view of the end effector of the present disclosure taken along line 21-21 in FIG. 20;

FIG. 22 illustrates the area of detail indicated in FIG. 21;

FIG. 23 is side a cross-sectional view of portions of the end effector of the present disclosure;

FIG. 24 illustrates the area of detail indicated in FIG. 23;

FIG. 25 is a perspective view of the end effector of the present disclosure in an approximated position; and

FIG. 26 is an end cross-sectional view of the end effector of the present disclosure taken along line 26-26 in FIG. 25.

DETAILED DESCRIPTION

Embodiments of the presently disclosed surgical instrument, loading unit for use therewith, and cartridge assembly for use therewith, are described in detail with reference to the drawings, wherein like reference numerals designate corresponding elements in each of the several views. As is common in the art, the term “proximal” refers to that part or component closer to the user or operator, e.g., surgeon or physician, while the term “distal” refers to that part or component farther away from the user.

A surgical instrument of the present disclosure is indicated as reference numeral 100 in FIG. 1. Generally, surgical instrument 100 includes a handle assembly 110, an elongated portion 120 extending distally from handle assembly 110, and a loading unit 200 disposed adjacent a distal end of elongated portion 120. While FIG. 1 illustrates surgical instrument 100 including a powered handle assembly, other types of handles can be used such as, for example, motor-driven, hydraulic, pivoting, ratcheting, etc. As used herein, “handle assembly” encompasses all types of handle assemblies. Loading unit 200 is releasably attachable to elongated portion 120 of surgical stapling instrument 100, e.g., to allow surgical instrument 100 to have greater versatility. This arrangement allows the clinician to select a particular loading unit 200 for a given procedure. As used herein, “loading unit” encompasses both single use loading units (“SULU”) and disposable loading units (“DLU”). Additionally or alternatively, surgical instrument 100 may have a cartridge that is removable and replaceable in the reusable jaws of the instrument.

Examples of loading units for use with a surgical stapling instrument are disclosed in commonly-owned U.S. Pat. No. 5,752,644 to Bolanos et α1., the entire contents of which are hereby incorporated by reference herein. Further details of an endoscopic surgical stapling instrument are described in detail in commonly-owned U.S. Pat. No. 6,953,139 to Milliman et α1., the entire contents of which are hereby incorporated by reference herein.

In surgical instrument 100 in accordance with the present disclosure, a firing rod (not explicitly shown) is moved distally through actuation of handle assembly 110 to deploy fasteners 600 (FIG. 7). With reference to the embodiment illustrated in FIG. 1, at least a partial actuation of first switch 112 or second switch 114 translates the firing rod longitudinally. Distal translation of the firing rod causes distal translation of a knife bar 140 (FIG. 23), which causes distal translation of a clamping member 500 to approximate at least one jaw member with respect to the other, as discussed in further detail below. Further, distal translation of clamping member 500 (FIG. 2) causes corresponding translation of an actuation sled 520 (FIG. 16), which results in pushers 550 causing the ejection of fasteners 600 (FIG. 17) from pockets 401 (FIG. 6) of a cartridge assembly 400.

With additional reference to FIGS. 2 and 3, loading unit 200 of the present disclosure is shown. Loading unit 200 includes a proximal body portion 210 defining a longitudinal axis “A-A,” and a tool assembly or end effector 220 including a first jaw member or anvil assembly 300 and a second jaw member or cartridge assembly 400. Cartridge assembly 400 includes a cartridge 408 disposed within a cartridge channel 409 (FIG. 7). Proximal body portion 210 is configured to be removably attached to elongated portion 120 of surgical instrument 100 as will be discussed in detail hereinbelow. As shown in FIG. 3, end effector 220 is pivotable with respect to the longitudinal axis “A-A.”

Referring now to FIG. 26, various features of loading unit 200 disclosed herein allow loading unit 200 to have a relatively small diameter “d” (such as, for example, about 4 mm, about 5 mm, about 6 mm, about 7 mm or about 8 mm) as compared with more conventional instruments having diameters of about 12 mm. The diameter “d” of the loading unit 200, and end effector 220 in particular, is measured between a radially outer-most wall of anvil assembly 300 (or top portion 502 of clamping member) and a radially outer-most wall of cartridge assembly 400 (or bottom portion 504 of clamping member 500). Such a low profile allows loading unit 200 to be inserted into trocars “T” (shown in phantom in FIG. 5) or other access devices having similar inner diameters. It is contemplated that the presently disclosed end effector 220 can be inserted into openings in body tissue (e.g., incision or naturally occurring orifice) having a comparable diameter. As can be appreciated, such low profile loading units 200 are useful in pediatric surgeries and/or other thin tissue locations, for example. Additionally, in the illustrated embodiments, a proximal portion 212 of proximal body portion 210 of loading unit 200 is sized and configured to engage elongated portion 120 of surgical instrument 100 (FIG. 1) having a larger-diameter elongated portion 120 (e.g., between about 7 mm and about 12 mm), thus enabling greater versatility by allowing the loading unit 200 to be coupled to instruments having an elongated portion 120 with an outer diameter between about 7 mm and about 12 mm.

More particularly, with reference to FIG. 2, an insertion tip 202 of loading unit 200 is linearly inserted into the distal end of elongated portion 120 of surgical stapling instrument 100 (FIG. 1). Nubs 204 of insertion tip 202 move linearly through slots formed adjacent the distal end of elongated portion 120. Subsequently, loading unit 200 is rotated about the longitudinal axis “A-A” such that nubs 204 move transversely with respect to longitudinal axis “A-A” through the slots within elongated portion 120. Additionally, during engagement of loading unit 200 and elongated portion 120, the firing rod of handle portion 110 engages knife bar 140 (FIG. 23) of loading unit 200.

With reference to FIGS. 7 and 26, clamping member 500 includes an I-shaped cross-section, including a top portion 502, which is configured to engage anvil assembly 300, a bottom portion 504, which is configured to engage cartridge assembly 400, and a vertical portion 503, which connects top portion 502 and bottom portion 504 and which may include a cutting edge 506 on its distal or leading surface. Further, distal advancement of clamping member 500 through end effector 220 causes top portion 502 to contact a camming surface 302 of anvil assembly 300 (FIG. 16). Continued distal advancement of clamping member 500 thus causes anvil assembly 300 to pivot with respect to cartridge assembly 400 from its open position (FIG. 4) toward its approximated position (FIG. 5). Further, top portion 502 of clamping member 500 is advanced distally within a slot 304 within anvil assembly 300, and bottom portion 504 of clamping member 500 is distally advanced within a slot 414 within cartridge channel 409 of cartridge assembly 400 to help stabilize the jaw members with respect to each other and to help maintain a constant gap between the first and second jaw members 300, 400. Thus, a predetermined amount of distal travel of the firing rod causes approximation and stabilization of jaw members. Additionally, cutting edge 506 of clamping member 500, if included on clamping member 500, travels through a channel 305 (FIG. 9) of anvil assembly 300, a channel 405 (FIG. 8) of cartridge assembly 400, and severs tissue disposed between the jaw members (and after the tissue has been fastened, as discussed above).

Additionally, with particular reference to FIGS. 13 and 14, a biasing element 540 is configured to bias anvil assembly 300 toward the open position. In particular, biasing element 540 (e.g., a spring) is disposed at or secured to a proximal end of anvil assembly 300. As shown in FIGS. 16 and 22, for example, biasing element 540 contacts a distal end 213 of proximal body portion 210. An end 542 (e.g., a cantilevered end) of biasing element 540 is urged proximally, thus biasing anvil assembly 300 toward its open position (FIG. 15).

With further regard to actuation sled 520, distal translation of actuation sled 520 sequentially engages a plurality of pushers 550, and causes pushers 550 to move toward tissue-contacting surface 410 (FIG. 8) of cartridge assembly 400 and eject fasteners 600 towards anvil assembly 300. Subsequent to the ejection of fasteners 600, cutting edge 506 of clamping member 500 severs the stapled tissue (FIG. 18).

With particular reference to FIGS. 11 and 12, further details of actuation sled 520 are disclosed. Actuation sled 520 includes two angled wedges 524 a, 524 b configured to contact either a first camming surface 560 or a second camming surface 561 of pusher 550, thus causing upper edges 553 of pushers 550 to engage fasteners 600, and subsequently cause ejection of fasteners 600 through retention cavities 450 of cartridge assembly 400 (FIG. 8), and toward respective pockets 320 (FIG. 10) of anvil assembly 300 (e.g., through tissue held between the jaw members).

Referring now to FIG. 12A, further details of pusher 550 are disclosed. Each pusher 550 includes a body portion 552, a lateral extension 554, a first leg 556, a second leg 558, a first camming surface 560, and a second camming surface 561. Each pusher 550 is positioned within cartridge assembly 400 such that body portion 552 is parallel to the longitudinal axis “A-A” (see FIGS. 2, 7 and 8). Upper edge 553 of body portion 552 is configured and dimensioned to engage a backspan 602 of fastener 600. Lateral extension 554 extends perpendicularly from body portion 552. In the illustrated embodiment an upper edge 555 of lateral extension 554 is co-planar with upper edge 553 of body portion 552.

In the orientation illustrated in FIG. 12A, first leg 556 extends proximally from lateral extension 554, and second leg 558 extends distally from lateral extension 554. In this first orientation, pusher 550 is used in connection with inside rows “I1” and “I2” of fasteners 600 (FIG. 8). As can be appreciated, when the orientation of pusher 550 is rotated 180°, pusher 550 is in its second orientation and is used in connection with outside rows “O1” and “O2” of fasteners 600 (FIG. 8). Additionally, in the second orientation, first leg 556 extends distally from lateral extension 554, and second leg 558 extends proximally from lateral extension 554.

With continued reference to FIG. 12A, each of the first leg 556 and second leg 558 is generally wedge-shaped, and includes respective camming surfaces 560, 561 at its lower end and a planar surface 562 at its upper end. First camming surface 560 is disposed at a first angle α1 with respect to an axis defined by a lower surface 556 a of first leg 556, and second camming surface 561 is disposed at a second angle α2 with respect to the axis defined by the lower surface 556 a of first leg 556. The first angle α1 is the same as the second angle α2, and may be between about 20° and about 40°, for example. Larger and smaller angles are also contemplated.

When pusher 550 is in the first orientation (FIG. 12A), camming surface 560 of first leg 556 is configured to engage wedge 524 (wedge 524 a or 524 b, depending on the row, as discussed below) of actuation sled 520, while camming surface 561 of second leg 558 is configured to be free from engagement with camming surface 524 of actuation sled 520. That is, in the first orientation, camming surface 561 does not contact or engage wedge 524. When pusher 550 is in the second orientation, camming surface 561 of second leg 558 is configured to engage wedge 524 (wedge 524 a or 524 b, depending on the row) of actuation sled 520, while camming surface 560 of first leg 556 is configured to be free from engagement with wedge 524 of actuation sled 520. That is, in the second orientation, camming surface 560 does not contact or engage wedge 524.

Additionally, as shown in FIG. 8, pushers 550 are arranged in four longitudinal rows “R1,” “R2,” “R3,” and “R4” where rows “R1” and “R2” are staggered on a first lateral side of channel 405, and rows “R3” and “R4” are staggered on a second lateral side of channel 405. Here, camming surface 560 of first leg 556 of pushers 550 arranged in row “R1” are longitudinally aligned with camming surface 561 of second leg 558 of pushers 550 arranged in row “R2.” Similarly, camming surface 560 of first leg 556 of pushers 550 arranged in row “R3” are longitudinally aligned with camming surface 561 of second leg 558 of pushers arranged in row “R4.” Accordingly, each wedge 524 a, 524 b of actuation sled 520 is configured to engage two rows of pushers 550. More particularly, first wedge 524 a is configured to engage pushers 550 in rows “R1” and “R2,” while second wedge 524 b is configured to engage pushers 550 in rows “R3” and “R4.”

The pushers are the same in the rows R1, R2, R3, and R4, but are arranged in opposite orientations from adjacent rows. The first leg and second leg have camming surfaces that face in opposite directions to allow the pushers to be used in R1 and R2, for example, but in opposite orientation. The lateral extensions in adjacent rows extend in opposite directions. With the pushers in adjacent rows, such as pushers in R1 and R2 for example, the lateral extensions are accommodated with a small area because the pushers (and staples) are staggered with respect to one another.

With particular reference to FIG. 12A, planar surfaces 562 of first leg 556 and second leg 558 of pusher 550 are parallel to upper edge 553 of body portion 552, but are not co-planar with upper edge 553. It is envisioned that planar surfaces 562 contact or substantially contact an undersurface 407 within cartridge assembly 400 after pushers 550 are moved or cammed by actuation sled 520 (see FIG. 24). That is, undersurface 407 within cartridge assembly 400 limits the travel of pusher 550 toward anvil assembly 300, which may be helpful for ensuring the complete and proper formation of fasteners 600, and may also be helpful to ensure pushers 550 remain within cartridge assembly 400 (e.g., before, during, and after ejection of fasteners 600).

Referring back to FIG. 8, retention cavities 450 of cartridge assembly 400 are shown. Each retention cavity 450 is T-shaped as it intersects tissue-contacting surface 410 to accommodate the travel of pusher 550 at least partially therethrough. Additionally, similar to pushers 550, adjacent rows of retention cavities 450 are longitudinally staggered from each other, and the orientation of retention cavities 450 is rotated 180° from retention cavities 450 in one adjacent row (see FIG. 8, for example). It is envisioned that the T-shape of retention cavities 450 helps maintain the lateral and longitudinal position of pushers 550 within cartridge assembly 400.

While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the present disclosure, but merely as illustrations of various embodiments thereof. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. A loading unit configured for engagement with a surgical instrument, the loading unit comprising: a proximal body portion defining a longitudinal axis; an end effector disposed in mechanical cooperation with the proximal body portion, the end effector including a cartridge assembly and an anvil assembly, one of the cartridge assembly and the anvil assembly being movable with respect to the other of the cartridge assembly and the anvil assembly between an open position and an approximated position to capture tissue therebetween, the cartridge assembly configured to house fasteners therein; an actuation sled longitudinally translatable within the cartridge assembly; and pushers disposed within the cartridge assembly, the pushers arranged in first and second rows, each pusher including a surface configured for engagement with the actuation sled, wherein the camming surface of each pusher in the first row is longitudinally aligned with the camming surface of each pusher in the second row, the first row of pushers laterally offset from the second row of pushers.
 2. The loading unit according to claim 1, wherein the camming surface of each pusher includes a first camming surface and a second camming surface.
 3. The loading unit according to claim 2, wherein the actuation sled is configured to contact the first camming surface of each pusher in the first row during distal translation of the actuation sled, and the actuation sled is configured to contact the second camming surface of each pusher in the second row during distal translation of the actuation sled.
 4. The loading unit according to claim 3, wherein the second camming surface of each pusher in the first row is spaced apart from the actuation sled during distal translation of the actuation sled, and the first camming surface of each pusher in the second row is spaced apart from the actuation sled during distal translation of the actuation sled.
 5. The loading unit according to claim 1, wherein the pushers include a lateral extension that is elongate in a vertical direction and the cartridge assembly includes T-shaped retention slots, the lateral extension being received in a portion of the T-shaped retention slot.
 6. The loading unit according to claim 5, wherein the actuation sled includes a first wedge and a second wedge, and distal translation of the actuation sled causes the first wedge to contact the first camming surface of each pusher in the first row and the second camming surface of each pusher in the second row, and distal translation of the actuation sled causes the second wedge to contact the first camming surface of each pusher in the third row and the second camming surface of each pusher in the fourth row.
 7. The loading unit according to claim 1, wherein an outer-most diameter of the end effector is about 5 mm.
 8. The loading unit according to claim 1, wherein an outer-most diameter of the end effector is selected from the group consisting of about 4 mm, 5 mm and 8 mm.
 9. The loading unit according to claim 1, further comprising a plurality of T-shaped retention slots extending through a tissue-contacting surface of the cartridge assembly.
 10. The loading unit according to claim 1, wherein each pusher in the first row is disposed in a first orientation and each pusher in the second row is disposed in a second orientation, the first orientation is offset 180° from the second orientation.
 11. The loading unit according to claim 1, wherein each pusher in the first row is the same as each pusher in the second row.
 12. The loading unit according to claim 2, wherein the first camming surface is disposed at a first angle with respect to the longitudinal axis, the second camming surface is disposed at a second angle with respect to the longitudinal axis, and the first angle is the same as the second angle.
 13. The loading unit according to claim 12, wherein the first angle is between about 20° and about 40°.
 14. The loading unit according to claim 2, wherein each pusher includes a body portion including an upper edge configured to engage a fastener, a lateral extension extending perpendicularly from the body portion, a first leg extending in a first direction from the lateral extension and including the first camming surface, and a second leg extending in a second direction from the lateral extension and including the second camming surface.
 15. The loading unit according to claim 14, wherein the upper edge of the lateral extension is co-planar with the upper edge of the body portion.
 16. A pusher for use with a surgical instrument, comprising: a body portion including an upper edge configured to engage a fastener; a lateral extension extending perpendicularly from the body portion; a first leg extending in a first direction from the lateral extension and including a first camming surface; and a second leg extending in a second direction from the lateral extension and including a second camming surface.
 17. The pusher according to claim 16, wherein an upper edge of the lateral extension is co-planar with the upper edge of the body portion.
 18. The pusher according to claim 16, wherein the first camming surface is disposed at a first angle with respect to the longitudinal axis, wherein the second camming surface is disposed at a second angle with respect to the longitudinal axis, and wherein the first angle and the second angle are the same.
 19. The pusher according to claim 18, wherein the first angle is between about 20° and about 40°.
 20. The pusher according to claim 16, wherein the first direction is opposite from the second direction. 